Gas turbine starter control system



Oct. 17, 1961 M. P. wooDwARD, JR 3,004,387

GAS TURBTNR STARTER CONTROL SYSTEM Filed April 27, 1959 1 i lll JNVENToR. M0670 waan/4eme BY T .Vurlwll O me l complex than system-s heretofore available.

Patented Oct. 17, 1961 tice 3,004,387 GAS TURBINE STARTER CONTRGL SYSTEM Morton Powell Woodward, Jr., Manchester, Mass., as-

signor to General Electric Company, a corporation of New York Filed Apr. 27, 1959, Ser. No. 808,983 4Claims. (Cl. 6039.14)

My invention relates to gas turbine starters and vin particular to control systems for gas turbine starters of the fuel air type.

As is well known in the art, it is a common practice to utilize gas turbine starters which may operate, for instance, on the products of combustion of fuel and air for the purpose of starting gas turbine engines. ln a typical installation the turbine starter is connected through suitable gearing to drive the rotor of the engine up to a preselected speed level in excess of the self-sustaining speed of the engine. The starting cycle is initiated by actuating a control which initiates the flow of fuel and air to the combustion system of the starter and at the same time activates the starter ignition system to initiate combustion in the combustion chamber. Once combustion is achieved, the ignition system i-s ie-energized, usually by means of a switch operated by the attainment of a preselected pressure in the combustion chamber of a level suliiciently high to indicate that combustion has occurred. The ow of hot gases from the starter combustion charnber tothe starter then continues until the engine has been driven to the preselected speed at which point the speed control element of the starter, usually lan electrical switch, is v.actuated to cut olf the supply of Ifuel and air to the combustion chamber, ending the starting cycle.

It is generally considered desirable in gas turbine starter systems of the foregoing type to permit the pilot or other operator toclose a single switch to initiate the starting cycle and to allow the switch to remain closed upon completion of the cycle without producing a recycling of the starter. With such a system it becomes unnecessary for the pilot to deactivate the control or take any further action once the start cycle is initiated. Such a system is also desirable from the standpoint of avoiding accidental recycling of the system, because in order to cau-se recycling, it is necessary for the pilot to irst return the switch 4to the off position and then move it back to the on position again, a two-step procedure which is diicult to accomplish accidentally. In addition, it is usually required that a provision `be made for allowing operation of the starter on air alone-a mode of operation commonly called air motoring. This mode of operation is convenient in many installations for a number of maintenance and checkout purposes which may require rotation of the engine at a low speed where it isnot desired to initiate the full start cycle of the system'.

The foregoing requirements are generally fulfilled by a number of fuel air starter control systems which have been in use for some time. However, these systems :generally require the utilization of a relatively large number of relays, and other contributing complexities in order to satisfy all of the foregoing requirements.- It will be appreciated, therefore', that the provision-cfa control which performs all of the requiredfunctions but which is less complex, lis desirable from .the standpoint of reducing the size, weight and cost of such systems andimproving their reliability. 4 4

In view ofthe foregoing, itis an object of my invention vto provide an yimproved control *system for fuel-air type gas turbine starters. 'i

'It is another object 'of my invention to provide-an improved controlv system of the foregoing .type which is less Briefly described, I accomplish the foregoing and other objects of my invention in one embodiment thereof by the provision of a system which requires only a single relay for each mode of operation; that is, one relay to control the normal starting cycle and la second relay to control the air motoring mode of oper-ation. 'Ihe coil of the normal start control relay is shunted at the initiation of the cycle through the contacts of a pressure-'actuated switch connected to respond yto the attainment of combustion in the starter combustion chamber. In addition, the system is connected such that the fuel and air supplies and the ignition system are all directly actuated by the closing of the pilots start switch to initiate the cycle. The attainment of combustion pressure in the combustion chamber actuates the pressure switch opening the shunt around the relay coil, thereby energizing the relay. The energization of the relay reconnects the circuit to lock the relay in, `de-energize the ignition system, and reconnect the power to the fuel and air controls through the pressure switch and a speed control switch, which opens when the preselected starting speed is reached. The opening of the speed control switch thus interrupts the power to the fuel and air controls to interrupt combustion, thereby causing the pressure switch to return to its original position to lock open the circuit to the fuel and air controls. Thus, upon completion of the start cycle, the system is locked in a condition Where recycling cannot occur without first rearming the system by opening the pilots switch and returning the relay to its original position. A separate relay is provided for energizing only the air controls in order to allow air motoring of the system.

A better understanding of my invention together with an appreciation of further objects yand advantages thereof may be derived from the following description taken in connection with the accompanying drawings in which:

The single figure is a schematic presentation of a fuelar starter, together with an associated control system embodying my invention.

Referring now to the drawing, there is shown an aircraft engine fuel-air starter 10 which comprises a combustion chamber 11 connected to supply the products of combustion of fuel and air to a turbine 12 through one or more inlet nozzles 13. The products of combustion are exhausted through a -suitable exhaust duct 14 connectible at flange means 15 with the exhaust ducting of the airplane. The turbine is connected to an output spline 16 through a suitable gear reduction 17, the output spline 16 being engageable with the mechanical input connection of a jet engine for starting purposes.

The system is provided with a fuel supply source, which may be in the form of a pressurized container 18, connected to the combustion chamber 11 through suitable conduit means 19 and 20 and a fuel liow control valve Z1. The iiow control valve 21 is solenoid operated by means of a solenoid 22 to control fuel ow through the conduits 19 and 20 -to the combustion chamber 11.

AThe valve 21 is spring loaded to the closed position so that energization of the solenoid 22 moves the valve to the open position to permit fuel flow and de-energization of the solenoid allows ythe valve to return to the closed position, thereby cutting olf fuel ow. Fuel flowing v through the conduit 20 is injected into the combustion .a spark plug 32 electrically connected to an ignition unit 33 by suitable electrical conductor means 34 and 35, conductor 35 being connected to the common ground of the system. The ignition unit is supplied with a direct current input atthe bus voltage of the system usually in the neighborhood of 18 to 32 volts and transforms this to` an ignition voltage level supplied to the spark plug lby conductor means 34 and 35. In la typical start cycle, once the ignition system has initiated combustion,

it is cut out of the system by operation of a pressure switch 36, as |will be hereinafter described.

The pressure switch 36 is represented schematically as a switch arm 37 operated by a pressure responsive bellows 38 to establish electrical contact either between contacts 39 and 40 or between contacts 39 and 41. The pressure t switch 36 is of the snap acting type so Ithat it is operable only between the contact positions shown, the existence of intermediate positions where no circuit continuity between either set of contacts exists being o nly transient and of only insignificant time duration. The pressure switch 36 is connected to respond to the pressure in the combustion chamber 11 by means of a conduit 42.

The pressure in the combustion chamber 11 is'substantially higher when combustion has been established than when fuel and air are supplied to the combustion `chamber without combustion taking place. In a, typical installation, for instance, the combustion chamber pressure for -fuel and air being supplied without combustion would be substantially less than that established by the air pressure regulator lvalve 29, being typically in the order of 200 p.s.i. For the same installation the establishment of combustion would increase the combustion ,chamber pressure to something in the vicinity of 350 to 400 p.s.i. 4For combustion chamber pressure levels in the vicinity of or less than about 280 p.s.i. in a typical installation, the pressure switch remains in the position shown, establishing electrical continuity between the contacts 39 and 40, and for pressures in the vicinity of that with a snap action to interrupt continuity between contacts 39 and 40 and establish continuity between contacts '7, produced by combustion, the p-ressure switch moves The normal start cycle of the system is controlled by means of a relay comprising a single coil A and contacts A1, A2, and A3. The air motoring mode of operation is controlled by a second relay which comprises a coil B and three sets of contacts, B1, B2, and B3. The conditionof each of the contacts, that'is whether they are in the normally open or normally closed position, is represented in each case for the system in the condition shown with both of the switches 44 and 47 in the open position and the starter unit at rest. The operation of the system of FIG. l in a typical start cycle will now be described. f

The start cycle is initiated by closing the switch 44 to connect direct current power from the bus 45 to the control system. It will be observed that the closing. of switch 44 connects the bus power directly to air valve solenoids 30 and 31 through contact B2, speed control switch 43, Contact A3, and the associated linterconnecting couductors as shown, the circuit passing through contact point 41 on the pressure switch 36. The bus voltage is also connected to the fuel control valve solenoid 22 through contact B2, speed control switch 43, and contacts A3 and B3.

Thus, with the system at rest in the condition shown, the closing of the switch 44 directly connects control power to the air control solenoids 30 and 31 and to the fuel valve solenoid ZZto actuate these valves Iand initiate the flow of fuel and air to the combustion chamber 11. The closing of switch 44 also connects the -bus voltage to the ignition unit 33 through a shunt circuit around relay coil A comprising contact B2, speed control switch 43, contacts A3 and B3, pressure switch arm 37 extending between contacts 39 and 40, and contact A2, the circuit being completed through the system ground as shown.

lt will be noted that relay co-il A is not energized by the closing of switch 44 because the shunt path just described provides 4a very low resistance path around the coil which prevents any significant flow of current through the coil. The relay coil B is isolated from the system by its open contact B1 and the switch 47, which remains open throughout the startingV cycle.

After a brief interval, during which fuel and air are injected into the combustion chamber 11 with the ignition system energized, 'combustion occurs, thereby increasing the pressure in `the combustion chamber and actuating the pressure switch 36. Actuation of the pressure switch 36 moves the switch 4arm 37 from the position shown,

Ythereby'interrupting circuit continuity between the conpressure switch 36 as just described opens the shunt path type described thus far would begin with the initiation of flow of fuel and lair into the combustion chamber 11 by operation of the valves 21, 2S and 29, together with activation of the ignition system to produce combustion in the combustionchamber. Upon the establishment of combustion, the pressure switch 36 is activated to cut olf the ignition system. The now of hot gas from the combustion chamber 11 would then normally continue until the preselected cutout speed had been attained, at which point a speed control switch, `the contacts of which are represented lat 43, is actuated to cut off the ow of fuel and air to the combustion chamber, completing the starting cycle. The start cycle initiated by means of -a start switch 44, which is generally a'simple,

`two position on-off type lof switch, connected to supply power to the control system from the airplane direct current bus 45, which is supplied from a direct current source trated in theA usual manner. A second on-oif type switch 47 is provided for the Vpurpose of controlling the air motoring mode of operation.

around the relay coil A, thereby connecting the coil A directly in series with the ignition unit 33. The current v owing through coil A under these conditions is suflicient to actuatethe relay, thereby opening contacts AZ and A3 and closing contact A1.

The closing of contact A1 locks in the relay A by connecting the coil A directly to system ground on one side, the other side being connected to the bus 45 through switch 44. Thus, `once contact A1 has closed, the relay coil A will remain energized so long as the switch 44 remains closed. i The closing of contact A1 also removes the ignition unit33 from the system by shunting on its input to ground, kthereby de-energizing the ignition system.

In the foregoing sequence, vthe pressure switch arm 37 moves to its activated position establishing contact between contact points 39 and 41 .before contact A3 is opened by energization of relay coil A, so that the connectionof bus voltage to the air solenoids 30 and 31 and the fuel solenoids 22 is not interrupted. Thus, with the switch arm 37 establishing continuity between contacts y 39 and 41, power is supplied to fuel solenoid 22 through contact B2, speed control switch 43 and pressure switch arm 37, and to the -air solenoids 30 and 31 through the same circuit together with contact B3, which has remained in the closed position.

In addition, it should be observed that the energization of relay coil A and the operation of pressure switch 36 as just described reconnects the control power to the air and fuel solenoids through a circuit established by the pressure switch in its actuated position, such that the return of the pressure switch to its inactivated position will interrupt power to the fuel and air control solenoids. So long as combustion continues, however, hold- .ing the pressure lswitch in its actuated position, circuit continuity between the power source 46 and the fuel and air control solenoids is maintained, and the starter turbine 12 continues to be driven by the products of combustion delivered through nozzle means 13 from combustion chamber 11. Once the unit has -attained a preselected cutout speed, -a speed control mechanism 48 is actuated to open the speed control switch 43. The speed control mechanism may be of any well known type, such as a ilyball governor or a spring restrained eccentrically mounted mass which is caused to move to an off-center position upon the attainment of a preselected speed level.

The opening of the speed control switch 43 interrupts the connection between the bus 45 and the -air and fuel solenoids 30, 31, and 22, thereby causing the fuel control valve 21 and the air valves Z8 and Z9 to move to 'their closed positions to cut oi the ilow of fuel and air to the combustion chamber 11. This causes a drop in combustion chamber pressure to substantially the atmospheric level, causing deactivation of the pressure switch 36, thereby moving the switch arm 37 back to the position illustrated, -re-establishing continuity betweeen the contacts 39 and 40.

Upon interruption of combustion in combustion chamber 11, the speed of the starter turbine begins to decrease,

because of the removal of the driving power from it,

reclosing speed control switch 43 and eventually coasting down to a stop. However, because the pressure switch 36 has been deactivated before the speed decay begins and has returned to the position shown, and because contact A3 remains open, the reclosing of speed control switch 43 does not reestablish the power connection to the fuel and air solenoids.

Thus, it will be seen that the operation of the pressure switch and the subsequent operation of relay A in response to the attainment of combustion connects the circuit in such a manner that power to the fuel and air supplies may be interrupted either upon the attainment of the desired cutout speed or upon a loss of combustion pressure, such that upon operation of the speed control switch 43 and the resulting resetting of the pressure switch 36 to its deactivated position, the circuit between the direct current bus 45 and the fuel and air supplies is locked in the open position, with the ignition unit 33 being shunted out to ground. Therefore, in order to recycle the starter, it is necessary iirst to open the switch 44, interrupting the power to the relay coil A and allowing it to reset to its original condition, and then to reclose the switch to initiate the sequence described above.

It will be observed that, at any time during the start cycle, the switch 44 may be opened to abort the remainder of the cycle. Thus, the pilot or other operator retains control of the sy-stem throughout the cycle and may shut it down in the event of an equipment malfunction or for any other reason.

The air motoring mode of operation may be initiated by closing the switch 47, thereby energizing relay coil B to close contact B1 and open contacts B2 and B3. This connects control power to the air control solenoids 30 and 31 through switch 47, contact'Bl, speed control switch 43, and contact A3, thereby initiating the flow of air from the air supply 24 to the combustion chamber 11. It will be observed that no power may be supplied to the fuel solenoid 22 or to the ignition unit 33 because the contact B3 is in the open position and the pressure switch remains in the deactivated position. The system will operate on the air motoring mode -as long as the switch 47 remains in the closed position, or until either the air supply is exhausted or the cutout speed is exceeded, thereby opening the speed control switch 43. It will be observed that the air motoring mode may be established independently of the normal start cycle for so long as the switch 47 is allowed to remain closed. Opening of the lswitch 47 de-energizes relay coil Band allows contacts B1, B2 and B3 to return'to their original conditions, thereby interrupting the control power circuit to the air solenoids 30 and 31.

In order to absorb the electrical energy stored in the solenoid coils When the current to them is interrupted, a diode 49 is connected between the common input point to the solenoid coils and system ground. The diode is connected in such a manner as to present substantially an open circuit to the power applied to coils but form -a short circuit in the direction of the inductive pulse which occurs upon interruption of current. The provision of the Vdiode 49 reduces arcing at the speed control switch 43 upon interruption of the power to the fuel and air control solenoids. Y

It Will be observed from the foregoing that I have provided a control system for a fuel-air starter wherein the start cycle is sequenced by the operation of a single relay taken together with the starte-r condition signal elements comprising the pressure switch and the speed cutout switch. This is accomplished in the embodiment presented Iherein by initially shunting out the relay coil through a circuit established by the relay contacts and the pressure switch in its deactivated position such that activation of the pressure switch energizes the relay coil. The operation of the relay then reconnects the circuit through the pressure switch in its activated position such that a subsequent deactivation of the pressure switch leaves the circuit in a locked open position.

It will be appreciated that while I have presented one embodiment of my invention, I intend this to be descriptive rather than limiting in nature, and that various modiiications and changes may be made in the embodiment presented herein without departing from the true scope and spirit of my invention as defined in the appended claims,

What I claim as new and desire to secure by Letters Patent is:

l. In a fuel-air gas turbine starter having fuel and air supplies connected through control means to a combustion chamber arranged to deliver products of combustion of fuel and air to a turbine rotor and having ignition means for initiating` combustion in 'said combustion chamber, a control system for controlling the cycle of said starter comprising relay means including an actuating coil and at least three sets of contacts operable upon energization of said coil, means for connecting a source of electrical energy to said coil, pressure responsive switch means connected to respond to the pressure in said combustion chamber, said pressure responsive switch means establishing a closed circuit path when in the inactivated position and being responsive to an increase in thev pressure in said combustion chamber beyond a preselected level corresponding to combustion yin said combustion chamber to interrupt said closed circuit path, speed responsive switch means connected to respond to the speed of the starter and establishing a closed circuit path when said speed is below a preselected level and an open circuit path when said speed is above said preselected level, rst electrical connecting means interconnecting said speed responsive switch means, said pressure responsive switch means, and iirst and second sets of 4'said relay contacts in a shunt path around said relay coil to shunt out said coil and thereby prevent energization thereof, second electrical connecting means electrically connecting a third set of said relay contacts to said relay coil so as to lock said relay in when said coil is energized upon the openingpof said shunt path, said first and secon-d setsvrof contacts being in the normally closed position and said third set of contacts being in the normally open position when said relay coil is de-energized, thirdl electrical connecting means for connecting said electrical energy source to said ignition means through said iirst electrical connecting means through a parallel path formed in one leg thereof by said relay coil and in the other leg thereof by said speed responsive switch means, said pressure responsive switch means and said first and 'second'sets of relay contacts, and fourth electrical con- `tion of fuel and air to a turbine rotor and having ignition means for initiating combustion in said combustion chamber, a control system for controlling the cycle of said starter comprising relay means including an actuating coil and at least one set of contacts operable on energization of said coil, switch means'for connecting a source of electrical energy to said coil, pressure responsive switch means connected to respond to the pressure in said combustion chamber, said pressure responsive switch means establishing a closed circuit path when in the inactivated position and being responsive to an increase in the pressure in said combustion chamber beyond a preselected level corresponding to combustion in said Vcombustion chamber to interrupt said closed circuit path, speed responsive switch means connected to respond to the speed of the starter and establishing a closed circuit path when said speedv is below a preselected level and an open circuit path when said speed is above said preselected level, frst electrical conductor means interconnecting said pressure responsive switch means, said speed responsive switch means, and said one set of contacts of said relay in a shunt path around said relay coil to shunt out said coil and thereby prevent energzation thereof, whereby the opening of said pressure responsive switch means or said speed responsive switch means opens said shunt path to energize said relay coil and open said one set of contacts to maintain said shunt path open and said relay energized until said coil is'disconnected from said electrical energy source, second electrical connecting means for connecting said electrical energy source lto said ignition system through said first electrical connecting means through a parallel path formed in one leg by said relay coil and in the other leg by said shunt path, and third electrical connecting'means for connecting said electrical energy source to said fuel and air controls through said rst electrical connecting means through another parallel path formed in one leg by said speed responsive switch means and in the other leg by said relay coil, said relay` contacts, and said pressure responsive switch means. o

3. In a fuel-air gas turbine starter having fuel and air supplies connected through control means to a combus- 8 tion chamber arranged to deliver products of combustion of fuel and air to a turbine rotor, a control system for .controlling the `cycle of` said starter comprising relay means including an actuatingA coil and at least two sets of normally closed contacts movable to the open position upon energization of said coil, switch means for connecting a source'of electrical energy to said coil, pressure responsive switch means connected to respond to the pressure in said combustion chamber, said pressure responsive switch means assuming an inactivated position when the pressure in said combustion chamber is below a preselected level corresponding to combustion in said combustion chamber andV an activated position when said pressure is above said preselected level and includking iirst and second circuit paths, said first circuit path being closed and said second circuit path being open `when said pressure responsive switch means is in the inactivated position, said first circuit path being open yand said second circuit path being closed when said pressure responsive switch means is Vin the activated position, speed responsive switch 4means connected to respond to the speed of the starter and establishing a closed circuit path when said speed is belowa preselected level and an open circuit path when said speed is above said preselected level, tirst electrical connecting means interconnecting said speed responsive switch means, said first and second( sets of relay contacts, and the closed circuit path established by said pressure responsive switch means in its inactivated position in a shunt path around said relay coil to shunt said coil and thereby prevent energization thereof, Second electrical connecting means connecting ,said first set of relay contacts in parallel relationship with the closed circuit path established by said pressure switch means in its activated position, and third electrical connecting means for connecting said electrical energy source to said fuel and air controls through said iirst elec- Y trical connecting means through a parallel path formed in one leg by said relay coil, said second set of relay contacts, and the closed circuit path established by said pressure responsive switch means in its inactivated position, and in the other leg by said speed responsive switch means and said first set of relay contacts.

4. Apparatus as set forth in claim 3 including fourth electrical connectingmeans for connecting said electrical 45,

energy source only to said air control comprising second relay means including an actuating coil and at least iirst and second sets of normally closed contacts operable to the open position upon energization of said coil, said iirst and second sets of contacts of said second relay means being connected in series with said shunt path around said first mentioned relay coil, one of said sets of contacts being connected to isolate said first mentioned relay coil from said power source upon energization of said second relay coil therefrom, and the other of said sets of contacts being connected to isolate said fuel control from said power source upon energization of said second relay coil.

References Cited in the iile of this patent 

